Hi!
I believe this might be a bug - onBeforeEventSegmentDrag seem to be missing the necessary context from which the drag was initiated (eventRecords).
See video.
Tested here: https://bryntum.com/products/schedulerpro/examples/infinite-scroll-crudmanager/
With this snippet in the console:
schedulerPro.on("beforeeventsegmentdrag", (e) => console.log("hello", e))